1. Field of the Invention
The present invention relates to a signal trap device and method, a recording medium replay device and method, and a signal extraction device and method, and more particularly to those adapted for use in separating an audio FM signal, which is recorded on a magnetic tape, from a luminance FM signal.
2. Description of the Related Art
FIG. 29 shows a spectrum of signals recorded on a magnetic tape in an 8 mm-tape video cassette recorder (trade name). As shown in the diagram, there is recorded, in the highest frequency band, an FM luminance signal obtained through frequency modulation of a predetermined carrier with a luminance signal. A carrier of 743.444 kHz, which is lower in frequency than the FM luminance signal, is amplitude-modulated with a low-frequency converted chroma signal. And in a band further lower in frequency than the low-frequency converted chroma signal, there is disposed a four-frequency tracking pilot signal (ATF signal).
Moreover, between the FM luminance signal and the low-frequency converted chroma signal, there are disposed an FM audio signal obtained through frequency modulation of a carrier of 1.5 MHz with the sum (L+R signal) of left (L) and right (R) stereo signals, and also an FM audio signal obtained through frequency modulation of a carrier of 1.7 MHz with the difference (L-R signal) of the stereo signals.
Since these signals are recorded on a magnetic tape after being processed through frequency multiplexing, the original signals can be reproduced by trapping signals of any unrequired frequency bands, then extracting the signals of desired frequency bands and executing frequency demodulation of the extracted signals.
For example, when the FM luminance signal (hereinafter referred to as YFM signal) is separated from the replay signal reproduced from the magnetic tape, the FM audio signal (hereinafter referred to as AFM signal) is first trapped by an LC tuning type AFM trap circuit consisting of a resistor 1, a coil 2 and a capacitor 3 as shown in FIG. 30A, or by an LC tuning type AFM trap circuit consisting of a coil 11, a capacitor 12 and a resistor 13 as shown in FIG. 30B.
More specifically, the AFM trap circuit shown in FIG. 30(A) or 30(B) is so formed as to widely attenuate the signals of frequency bands of 1.5 MHz and 1.7 MHz, wherein the AFM signal is trapped from the reproduced replay signal.
Further the YFM signal is extracted from the replay signal where the low-frequency converted chroma signal and the ATF signal have already been trapped, and then the YFM signal thus extracted is demodulated.
With regard to the frequency deviation .DELTA.w of the FM signal and the modulation angular frequency p thereof, the exclusive bandwidth of the frequency-modulated waves becomes approximately 2(.DELTA.w+p). Therefore, in order to trap the FM signal with any frequency deviation from the replay signal reproduced from a magnetic tape, it is necessary in the related art to trap the frequency band of a considerably wide range including 2(.DELTA.w+p). As shown in FIG. 29, the frequency bands of the AFM signal and the YFM signal are very close to each other. For this reason, in trapping the AFM signal from the reproduced signal, the low-frequency band component of the YFM signal is also trapped to consequently deteriorate the resolution with another disadvantage of hardly attaining a high-quality picture.
Furthermore, if the circuit is so formed as to sharply trap only the center frequency of the carrier of the AFM signal, an AM component is generated in accordance with the frequency deviation of the FM signal to eventually cause horizontal streaks with shading on the screen.
It has been customary heretofore that such disadvantages are existent also in a Betamax video cassette recorder (trade name) for example.